In recent years, there has been a strong increase in demand for shortening and accelerating the development processing in the fields of silver halide photographic light-sensitive materials, such as color printing paper. At the same time, there is also demand for reduced cost, and enhanced performance, such as higher-quality image.
As a silver halide emulsion that is to be used for color printing paper, silver halide emulsions with high-silver chloride content have been used, to cope primarily with the aforementioned demand for acceleration. However, light-sensitive materials having high-silver chloride content have the drawbacks that they are low in sensitivity and that they are apt to cause fogging.
Various improvements in, for example, chemical sensitizing methods and silver halide emulsion grain formation methods have been made for high sensitization of high-silver chloride emulsions. As typical methods of chemical sensitization of silver halide emulsions, various sensitization methods, such as sulfur sensitization, selenium sensitization, tellurium sensitization; noble metal sensitization using, for example, gold; reduction sensitization, and combinations of these sensitization methods, are known. As a selenium sensitizer used in a selenium sensitization method, among the above sensitization methods, use of a selenocarboxylate, i.e. seleno ester, is known (see, for example, U.S. Pat. Nos. 3,297,446, 3,297,447, and JP-B-57-22090 (“JP-B” means examined Japanese patent publication)).
In the case of color printing paper, it is preferable to use a silver halide emulsion that is reduced in fogging to the lowest extent, in order to express white color attractively. Selenium sensitization sometimes produces a larger sensitizing effect than sulfur sensitization used in the fields concerned. However, this selenium sensitization conspicuously increases occurrence of fogging, and also is apt to result in increase in gradation softness, and therefore it is unsuitable to color printing paper. Also, when selenium sensitization is utilized together with gold sensitization, a significant sensitivity increase is attained. However, fogging is largely increased at the same time, and also the resultant prints are apt to result in increase in gradation softness. As such, there has been a strong need for development of a selenium sensitization method that is reduced in generation of fogging and that provides a high-contrast or hard-gradation print.
Further, in a production process, silver halide emulsions, various emulsified dispersions, various additives, and the like are mixed and dissolved, and then applied. With a large production scale, and due to coating problems, or the like, these emulsions, dispersions, and additives are required to be left in a solution state for several hours. A large factor in production stability is to reduce the change in performance with the lapse of time after these materials are mixed and dissolved.